1. Technical Field
This application generally relates to X-ray generation equipment, and more particularly to a small, lightweight, and power-efficient X-ray source module.
2. Description of Related Art
Devices including X-ray systems are used in the field for a variety of purposes including, for example, XRF (X-ray fluorescence) analysis of metals, ores, soil, water, paints and other materials, identification of taggant materials for security purposes, and analysis of materials in bore holes. Until recently, field-portable XRF instruments used radioactive sources, such as Cd-109, to provide the required X-ray flux. However, the intensity of a radioactive source decays with time requiring frequent recalibration, and radioactive sources are subject to strict regulatory control with respect to transportation, storage and disposal. Moreover, a radioactive source cannot be turned off when not in use, further exacerbating the safety issues associated with such a source. As an alternative to the radioactive source, the devices may include X-ray systems that use an electronic X-ray source for XRF and other X-ray analytical applications. X-ray sources that operate at power levels of 5 watts or less at voltages in the range of approximately 5-100 kV are known to fulfill the intensity and spectral requirements for most field-portable X-ray instruments. For practical considerations, it may be desirable to have a field-portable X-ray source that is small and lightweight, fits into an ergonomic hand-held enclosure, is powered from a lightweight battery such as a dry cell, and incorporates radiation shielding to prevent stray radiation from the X-ray tube from reaching the operator. Furthermore, it may be desirable to have the X-ray source voltage and current be highly regulated, (e.g., such as better than a 0.1% variation), to provide a stable X-ray beam of predetermined intensity. It may also be desirable to have a device such that the operating parameters of the device can be externally controllable by other electronic circuits contained within the instrument. Conventional X-ray tubes and their associated electronics are typically designed to operate at much higher power levels of 50 watts and above. They are too bulky, too heavy, and require too much electrical power for field-portable applications. Therefore, there is a need for a high accuracy and stability, low-power, lightweight, compact, radiation shielded X-ray source for use in XRF instruments and other portable and hand-held X-ray analytic instruments.
Radiation shielding of a hand-held X-ray generating device is particularly difficult. X-ray shielding usually takes the form of a layer of high atomic number, high density material, such as lead, tungsten, or molybdenum surrounding the X-ray source. Since an X-ray tube operating at 5-100 kV emits X-rays uniformly in all directions from the electron beam focal spot on the X-ray target, emission in directions other than along the desired X-ray beam direction must be shielded. In practice, some shielding is provided by the walls of the X-ray tube itself, and by the coolant fluid (if any) and electrically insulating material that surrounds the X-ray tube, but this is usually not sufficient to prevent exposure of personnel in close proximity to the tube. In order to minimize the total mass of shielding material, it may be desirable to have the shielding material mounted as close to the source of X-rays as possible. However, this is usually not possible in practice due to the presence of the coolant fluid and electrical insulation mentioned above. Furthermore, if shielding is provided by an external housing formed from radio-opaque material, extreme care must be taken to eliminate any cracks or seams in the housing. Satisfactory shielding is typically accomplished by providing a region of overlap at every seam, further increasing the total weight of the shielding material. Extreme care must also be taken to ensure that the shielding material cannot shift relative to the source of X-rays. This is particularly important in a portable unit that may be subject to large mechanical and thermal stresses in the field.
Thus, it may be desirable to have a low-power X-ray system that may be used for field applications which overcomes the drawbacks of existing systems.